1. Technical Field
The present invention relates to a printing apparatus, and a method and program for controlling the printing apparatus and, in particular, to a technique of measuring a consumption of a colorant during printing.
2. Related Art
In a printing apparatus, the consumption of a colorant has been measured and then referred to as a criterion whether to perform a cleaning operation or a colorant cartridge replacement operation on the printing apparatus. For example, Japanese Unexamined Patent Application Publication No. 11-221932 discloses a printing apparatus that measures a cumulative count of dots formed through ink jet ejection, and thus indirectly calculates an ink consumption. Japanese Unexamined Patent Application Publication No. 2001-199085 discloses a printing apparatus that measures beforehand an amount of ink consumed to print a typical document that is frequently printed by a user, and then determines based on the measurement data whether many copies of such a typical document can be printed when the remaining amount of ink becomes small.
A laser printing apparatus, in particular, measures a coverage duty as a print shade level, and presents an average coverage duty (%) to the user. The coverage duty is a ratio of a colorant sticking area to a print sheet, and, for example, to a colorant consumption with respect to an area of a sheet size A4 being 100%. More specifically, by multiplying the average coverage duty by the number of pages (print count), a colorant consumption (%) is calculated. If the service life of a colorant cartridge is 5000 sheets on 5% printing on a A4 sheet size, the amount of colorant to be consumed is 25000 (=500×5) (%). The ratio of the amount of the consumed colorant (in other words, the ratio of the amount of the remaining colorant) is predicted based on the amount of colorant to be consumed and the calculated amount of consumed colorant.
There are times when the actual colorant consumption and the print shade level (coverage duty) are related as illustrated in FIG. 8. More specifically, in normal printing jobs, such as printing tables or graphs, the print shade level is proportional to the actual colorant consumption. However, in low shade level printing such as text printing that is typically performed at a print shade level lower than C1, the print shade level is not proportional to the actual colorant consumption. Even if the print shade level is lowered, a waste amount of colorant simply increases, and the colorant consumption is at a substantially constant level L. With high shade level printing such as photograph printing performed in a region above a high print shade level Ch, the print shade level is not proportional to the actual colorant consumption. Even if the print shade level is raised, the colorant consumption does not increase but remains at a predetermined value H.
The colorant consumption, if converted from the above described print shade level, may fail to equal the actual colorant consumption. Although an average usage method and an average usage status of the printing apparatus can be clarified by calculating the average coverage duty, a usage status not reflecting the actual usage status is not known. The mere mean of the print shade levels (coverage duties) is not sufficient as data according to which whether to perform the cleaning operation and maintenance job is determined.